[#5942] Ensure TranslatorServiceFactory remains BC with < 2.3.0

- Only use the `DummyTranslator` if `ext/intl` is disabled, or if
  `'translator' => false` configuration is provided
- If no translator configuration is provided, and ext/intl is enabled,
  use a `Zend\I18n\Translator\Translator` instance to seed the
  `Zend\Mvc\I18n\Translator`.
Use --prefer-source flag for composer

- so that travis will be able to build properly
[#5942] skip some tests when ext/intl is not present

- When @ralphschindler ran using a PHP version that did not have
  ext/intl, these two tests failed. They should not run in that
  situation.
Merge #5942
Merge branch 'hotfix/mvc-translator-bc' of git://github.com/weierophinney/zf2 into hotfix/5942

* 'hotfix/mvc-translator-bc' of git://github.com/weierophinney/zf2:
  [#5942] skip some tests when ext/intl is not present
  Use --prefer-source flag for composer
  [#5942] Ensure TranslatorServiceFactory remains BC with < 2.3.0
Merging #5942
Merge branch 'hotfix/5942' into develop

* hotfix/5942:
  [#5942] skip some tests when ext/intl is not present
  Use --prefer-source flag for composer
  [#5942] Ensure TranslatorServiceFactory remains BC with < 2.3.0